Grid-connected Control Strategy for Grid-forming Converters Under Voltage Unbalanced Grid Conditions Based on Feedforward Correction

Grid-forming control is a solution to address the safety and stability issues brought about by the trend of "dual highs" (high proportion of renewable energy and high proportion of power electronics equipment) in power systems from the power source side. However, when the grid voltage is imbalanced, traditional grid-forming control methods fail to achieve normal grid connection. Therefore, a voltage feedforward correction grid-forming method based on the virtual synchronous generator is proposed. Based on the analysis of the VSG control algorithm, the voltage feedforward of the VSG in the dq0 coordinate system combined with the effective value balance analysis of the three-phase current on the α-β axis enables the VSG to achieve balanced control of the three-phase current in the voltage imbalanced grid. This method does not require specific transmission line parameters and can achieve balanced three-phase current under various operating conditions. Simulation results verify the effectiveness of this control strategy.